Conventionally, in various fields such as engineering and medical science, thermography is used to measure surface temperature of a measurement object noncontactingly. The thermography shows temperature distribution of a surface of an object or an organism as an image, and temperature detected by an infrared radiation thermometer is grasped as a change of electrical characteristics and is re-converted into strength of light and outputted as an image, whereby continuous temperature distribution of the surface of the measurement object can be observed.
For example, in the infrared radiation thermometer, (1) infrared radiation from a measurement object is condensed through a lens and focalized at a detecting element, (2) an electric signal corresponding to the strength of the infrared radiation is obtained from the detecting element, and (3) the signal is amplified, linearizedly revised and emissively revised by, and then displayed and outputted.
Such thermography is also used in the field of casting so as to measure temperature of a cavity of a casting mold.
Explanation will be given on an example of the casting processes referring FIG. 1. For example, the casting processes are performed in steps S1 to S4 shown in FIG. 1. A mold 30 is clamped (step S1), melted metal is injected into a cavity 33 so as to form a product (step S2), the mold is opened and the product is taken out from the mold 30 (step S3), the cavity 33 is splayed thereto with release agent and then dried by air blow (step S4), and then the mold 30 is clamped again (step S1) and the casting processes are shifted to the next cycle.
In the above casting processes, at the time of opening the casting mold, temperature of the cavity is measured with an infrared radiation thermometer 10. However, at the time of opening the casting mold, smoke, oil mist, the release agent and the like are scattered, whereby an objective lens 11 of the thermometer 10 is adhered thereto with oil, dust and the like and is contaminated. Accordingly, dirt is accumulated on the objective lens 11 of the thermometer 10 so as to cause measurement abnormality. Then, it is necessary to clean the surface of the objective lens 11 timely. For preventing contamination of a lens of an infrared radiation thermometer, the JP-U-3041996 discloses an art of an infrared radiation thermometer that a protection filter is detachably attached at a position before an objective lens so as to prevent adhesion of oil, dust and the like to the objective lens and to perform check of contamination and cleaning work quickly.
However, in the casting, at the time of measuring the temperature of the cavity of the casting mold, the objective lens of the infrared radiation thermometer may be positioned at a position difficult to be viewed by an operator, such as a position above the casting mold or a position with high temperature. In this case, it is difficult to judge whether the measurement abnormality is caused by the contamination of the objective lens actually or not. For preventing the measurement abnormality caused by the contamination of the objective lens, the surface of the objective lens may be cleaned usually, but it is not productive.
The present invention proposes an art of the infrared radiation thermometer used for thermography that measurement abnormality is detected and the cause of the measurement abnormality, such as contamination of the objective lens, defect of the mechanical part of the infrared radiation thermometer or the like, is estimated.